Steel, plated with copper, is utilized for a wide variety of applications. For example, copper plated steel wire is utilized for tire cord in steel radial tires, in high pressure hoses and belts and has other related applications.
Prior art electrolytic copper plating methods have utilized plating solutions commonly formed from copper pyrophosphate and copper sulfate. The copper pyrophosphate solution is understood to be pH neutral and is often preferred over the pH acidic solution of copper sulfate. No matter which solution is selected, however, prior art apparatus and methods have utilized soluble copper anodes.
For example, oxygen-free copper metal is usually utilized in a soluble anode in a copper pyrophosphate plating solution. The anode is placed on a positive charged electrode basket made of titanium or stainless steel. During plating, the anode changes shape. More specifically, copper dissolves from the anode to replace copper consumed from the solution to plate the steel. This change in shape, disadvantageously, results in relatively large variations in the current density at the steel being plated (functional cathode). This leads to uneven plating on the steel. Accordingly, plating quality is adversely effected.
An additional drawback to the utilization of soluble anodes is the need to periodically provide replacement as the copper of the anodes becomes exhausted. This is an inconvenient, relatively time consuming and usually unpleasant task. In many plating operations, it also may require some downtime which adversely effects productivity.
In others, and particularly continuous plating operations, "sparking" may occur during anode replacement. Sparking results when the anode simultaneously contacts both the electrode basket (positive charge) and the steel being plated (negative charge). Sparking creates a surface defect which is detrimental to the finish of the plated product.